The present invention relates to the field of cellular communication systems. More specifically, the present invention relates to defining the radio coverage areas of servers for use in cellular network planning tools.
As cellular communication has become more popular, cellular service providers have felt increasingly pressured to use the cellular radiofrequency (RF) spectrum as efficiently as possible. Greater efficiency allows a service provider to carry more calls using a given amount of RF spectrum. The problem of efficiently assigning the given amount of RF spectrum, i.e., channels, within a cellular network is a complex one.
Typically, a service provider is allocated a pool of channels for use within a network. The provider controls the assignment of the channels of the pool to various cells in the network. Automated approaches to network planning are being developed to assist service providers in devising channel assignment plans for cellular networks. Some automated network planning tools involve simulating the actual cellular network to predict the propagation of radiofrequency (RF) signals in order to define the radio coverage areas for the servers, e.g., base stations, to characterize potential interference within a simulated environment in order to effectively make channel assignments, to perform hand-off analysis, and so forth.
A realistic representation of the radio coverage areas for servers in the simulated cellular network is useful for subsequent related activities such as predicting carrier-to-interference ratios, hand-off analysis, channel assignment, macrocellular and microcellular planning, CDMA optimization, and so forth. Indeed, definition of the radio coverage areas is of particular interest at locations where two or more cells overlap.
Two or more cells may overlap along cell boundaries and along boundaries of sectors within a cell. In addition, overlap occurs when one cell, sometimes referred to as a microcell, is partially or wholly located within a larger cell, sometimes referred to as a macrocell.
In the simulated cellular network, associating servers with particular locations within the cellular network may be based on rigid selection criteria. For example, one selection criterion may be relative signal strength. That is, a radiofrequency signal may be transmitted from a first server and detected at a predetermined location. Another server then transmits a radiofrequency signal which is subsequently detected at the predetermined location. The server exhibiting the greater signal strength at that particular location is then determined to be the preferred, or better, server for that location.
When the signal strength of the signals transmitted from the servers and detected at the particular location are substantially equivalent, one simulation technique may be to arbitrarily select one of the two cells, or sectors, depending upon order of analysis to associate with a particular location. Such rigid selection criteria can introduce bias when defining the coverage area of a particular server. That is, if the selection algorithm is biased to consistently select one server over another in overlapping regions, a simulated radio coverage area for the one selected server will appear to be bigger than it actually is. Such a bias introduces error into the subsequent network planning activities because one cell or sector may appear busier than its overlapping cell or sector since the simulated radio coverage area has grown disproportionately large.
Server selection based upon relative signal strength is also problematic in areas having both microcellular coverage and macrocellular coverage. Macrocellular coverage is optimized to serve users moving in vehicles at relatively high speeds. Conversely, microcellular coverage is optimized for users, such as pedestrians, who are not moving at relatively high speeds. As a result, a microcell is typically a smaller geographic unit than a macrocell and a microcell server for the microcell typically transmits at a lower power level than a macrocell server. The use of microcells is desirable because the equipment for the microcell server is less costly due to the low transmission power requirements. In addition, the lower power transmission levels result in a more efficient use of the frequency spectrum because the channels used in the microcell can be reused closer to the microcell than a conventional macrocell channel reuse pattern.
Unfortunately, since the signal strength of the radiofrequency signal transmitted from the macrocell server is typically higher, the radiofrequency signal transmitted from the macrocell server may consistently dominate the radiofrequency signal transmitted from the microcell server in the simulated environment. Accordingly, bias for or against each of the macrocell and the microcell may be introduced when defining the radio coverage areas of each of the macrocell and the microcell.
Accordingly, it is an advantage of the present invention that an improved system and method are provided for associating a server with a location in a cellular network.
Another advantage of the present invention is that the system and method simulate radio coverage areas that approximate real world cellular network performance.
Another advantage of the present invention is that the system and method define the radio coverage areas to more closely portray the actual radio coverage area so that call traffic loads for overlapping cells may be accurately predicted.
It is yet another advantage of the present invention that the system and method of associating servers with locations substantially avoids the ill effects of bias.
The above and other advantages of the present invention are carried out in one form by a method of associating a server with a location in a cellular network. The method calls for detecting a first radiofrequency signal exhibiting a first power level at the location, the first radiofrequency signal being transmitted from a first server, and detecting a second radiofrequency signal exhibiting a second power level at the location, the second radiofrequency signal being transmitted from a second server. A proximity region is defined surrounding the location. When one of the first and second servers resides in the proximity region and a second one of the first and second servers resides outside of the proximity region, the method calls for selecting the one of the first and second servers residing in the proximity region to associate with the location.